Hops used in brewing mainly add bitterness and impart a hop flavor (e.g., taste and smell) to the final product. Hops derived from the fruit (cones) of hop plants are composed of soft resins, hard resins, hop oils, waxes, lipids, and carbohydrates. The soft resins consist of xcex1-acids and xcex2-acids. The soft resins and a hop oil fraction are extractable by organic solvents, or by liquid and supercritical CO2. In conventional brewing, the xcex1-acids are converted into iso-xcex1-acids, which are responsible for the bitterness taste. Although there is a lack of concensus as to how best to describe the character of hop flavor in beer, it is universally recognized that the hop flavor (or the kettle hop flavor) is an essential aspect of the total organoleptic impact of beer.
U.S. Ser. No. 08/838,217, now U.S. Pat. No. 5,972,411, which is incorporated by reference herein, disclosed that water soluble glycosides comprising an aromatic compound bonded to a mono-, di-, or trisaccharide may be extracted from hop or hop solids. The hop glycosides thus obtained are precursors to essences and flavorants and can be used to flavor beer. Hydrolysis of the glycosidic bond of the glycosides results in the formation of aglycons and free sugars. It is the volatile aromatic compounds that help confer flavor to beverages such as beer. Conversion of glycosides to their constituent aglycons and sugars can be achieved chemically by acid hydrolysis, enzymatically through the action of specific glycosidases, or fermentatively using whole cell biocatalysts such as yeast. The aromatic aglycons may be added to unhopped beer to impart a flavor after fermentation. The use of these kettle hop essences and flavorants provides economy, efficiency, consistency, flexibility, convenience, and quality to the brewing process.
The isolation of hop glycoside flavor precursors from hop cones as a source of flavorants used as additives to flavor beer was an improvement over the prior art. However, there remains a need for further improvements in the brewing process.
Traditionally, hops used in brewing are derived from the fruit or hop cones of hop plants, and the hop plant leaves and stems are discarded. However, the use of hop cones in brewing has certain disadvantages. The cones of hop plants contain certain hop resins, which can indirectly confer an excessively bitter taste to beer. Derivatives of hop resins are susceptible to degradation upon exposure to light, which results in the formation of compounds that impart an undesirable flavor to beer or similar beverages comprising the compounds. Therefore, beer containing hop resins is susceptible to staling or developing undesirable flavors over time, particularly if the beer is exposed to light.
There is an ongoing interest within the brewing industry to develop new methods that afford improved efficiency, cost savings, and processing advantages over prior art methods, or which yield a product having desirable characteristics, such as improved taste, reduced sensitivity to light, organ extended shelf life.
What is needed in the art is a method of isolating hop glycosides from hop plant parts that are substantially free of resins.
We have discovered that kettle hop flavor essence and flavorant precursors can be isolated from hop plant parts other than hop cones, including hop plant leaves and stems, at acceptable yields and essentially free of hop resins.
One aspect of the invention provides a kettle hop essence and flavorant precursor prepared from hop leaves or stems, and a method of making the precursor preparation, comprising the steps of extracting hop plant leaves or stems with an aqueous alcohol to produce an extract containing polar, water soluble compounds; concentrating the polar, water soluble compounds in the extract; and purifying the kettle hop essence and flavorant precursor in the concentrated extract.
Another aspect of the invention is a kettle hop essence and flavorant preparation, and method of preparing the essence and flavorant preparation from the essence and flavorant precursors of the present invention, the method comprising; the step of treating the precursors under conditions suitable to cause hydrolysis of the glycosidic bond between the aglycon and sugar moiety of at least a portion of the glycosides in the precursor.
Optionally, the kettle hop essence and flavorant preparation may be modified by adding to the preparation at least one hop fraction selected from hop oil, iso-xcex1-acids, dihydroiso-xcex1-acids, tetrahydroiso-xcex1-acids, and hexahydroiso-xcex1-acids. The kettle hop essence and flavorant preparation may be modified by adding to the preparation a kettle hop essence and flavorant derived from hop cones.
The invention includes a method of making kettle hop flavored beverages using the kettle hop essence and flavorant precursors, and a fermentable growth medium comprising the steps of adding a kettle hop essence and flavorant precursors of the present invention to the medium prior to fermentation.
The present invention includes beverages flavored with a kettle hop essence and flavorant preparation derived from essence and flavorant precursors isolated from hop plant parts other than cones, and methods of making the beverages comprising adding the preparation to the beverage in an amount sufficient to achieve the desired intensity and character of flavor. For beverages prepared from a fermentable growth medium, the flavorant preparation is preferably added after the medium has been fermented.
Optionally, the beverage of the present invention may be prepared using a kettle hop essence and flavorant that has been modified to contain at least one hop fraction selected from hop oil, xcex1-acids, iso-xcex1-acids, dihydroiso-xcex1-acids, tetrahydroiso-xcex1-acids, and hexahydroiso-xcex1-acids, or a flavorant derived from hop cones.
It is an object of the invention to provide a method that will allow hop plant parts other than hop cones to be used for preparing kettle hop essences and flavorants.
It is a further object of the invention to provide a method of preparing fermented beverages flavored with flavorant precursors extracted from hop plant leaves or stems or kettle hop essences and flavorants prepared by hydrolysing and/or fermenting at least a portion of the glycosides present in the essence and flavorant precursors of the present invention.
It is an advantage of the present invention that the yield of purified kettle hop essences and flavorants per hop plant is increased.
It is a further advantage that the hop stems and leaves from which the essence and flavorant precursors of the present invention are prepared contain essentially none of the resins that can contribute to excessively bitter taste, off flavor, and staling of fermented beverages.
It is a further advantage that kettle hop essence and flavorant precursors to be added into a fermentable beverage media prior to fermentation for preparing fermented beverages.
It is advantageous that by using hop plant leaves and stems the need for extraction of hops with organic solvents or liquid/supercritical CO2 used to remove hop oil and resins is eliminated, which simplifies the purification process.
Another advantage of the invention is that hops essences and flavorants prepared from precursors isolated from hop plant stems and leaves may confer a different desirable flavor to fermented beverages comprising the hops essences and flavorants than are provided by hops essences and flavorants derived from hops cones.
It is a further advantage that the method of the present invention increases the yield of hop flavorant precursor by using leaves and stems that are normally discarded.